Speciality beverages in which at least a portion is made up of frothed or heated milk are becoming more and more popular. The best-known beverage of this type is a coffee of the cappuccino type. It comprises a liquid portion consisting of coffee topped by a layer of frothed milk which, because of its very much lower density, floats atop the surface of the liquid. In general, preparing one takes time, manipulation operations and cleaning.
The most customary way of preparing a milk-based froth is to pour the desired amount of milk into the container, immerse a steam outlet pipe from a coffee machine in the container, agitating it up and down to introduce the air needed to form the froth.
There also exists mechanical stirring appliances which are usually intended for domestic use for beating froth from more or less viscous food products such as eggs, ice, juices or the like. These appliances are usually ill-suited to froth the microbiologically sensitive liquids such as milk. Regular cleaning of the tank of the appliance needs to be envisaged in order to remove any solid food residue. In addition, heating the milk has a tendency to increase the extent to which cooked or burnt proteins are deposited on and adhere to the surfaces. The existing appliances are not, for the most part, well suited to reducing the encrustation of this solid residue, making cleaning troublesome. These appliances also have a stirring and drive mechanism which is fixed and intrudes into the tank, and this presents several disadvantages: the removal/refitting time is not insignificant, they have a tendency to become soiled more quickly, they entail additional cost as a result of the multiplicity of components, and the stirring means are difficult to clean.
U.S. Pat. No. 6,318,247 relates to an appliance for preparing hot beverages or food with stirring such as hot chocolate, for example. Other devices for stirring food products are described in patent documents WO 2004/043213 or DE 196 24 648. Stirring systems with a magnetic engagement type are described in documents U.S. Pat. No. 2,932,493, DE 1 131 372, U.S. Pat. Nos. 4,537,332 and 6,712,497. DE 89 15 094 relates to a refrigerated pot for dispensing a milk-based beverage. U.S. Pat. No. 3,356,349 discloses a stirring device that has a heated tank, magnetic drive means positioned under the tank for driving a hub located in the middle of the tank.
An improved appliance for preparing froth from a milk-based liquid or milk has been proposed in WO 2006/050900, WO 2008/142154, WO 2011/039222 and WO 2011/039224. The device has: an inner tank for receiving the liquid that is to be frothed, in which a rotatable stirrer is positioned; an outer stand holding the tank; drive and control means which are in a cavity located between the inner tank and the outer stand, and which communicate with a switch and electrical connections located on the outer surface of the stand; and disturbance means to optimise circulation of the milk during frothing. In WO 2010/023313 a steam source is associated with the stirring effect.
More recently, it has been proposed, as described in WO 2009/074555 and WO 2011/144647, to provide a coffee machine with this type of milk conditioning tank.